The present invention relates to electrically controllable displays. In particular, the present invention discloses reflective displays which utilize ambient light and which have a wide angle of view.
In recent years, extensive research on electrically controllable display media has been performed. One type of display medium which has received considerable attention is fine-grained optically birefringent ferroelectric ceramics, as described in U.S. Pat. Nos. 3,499,704 by Land et al; 3,513,864 by Haertling et al; 3,531,182 by Land et al; and 3,609,002 by Fraser et al. One particularly advantageous ferroelectric ceramic material is lanthanum-modified lead zirconate titanate (PLZT).
A second widely studied type of display medium is liquid crystals, particularly liquid crystals of the nematic phase. Some of the many applications of liquid crystals are described by Fergason et al, "Liquid Crystals and Their Applications," Electro-Technology, 41 (January, 1970). Liquid crystals may operate in a variety of modes, including the birefringent and dynamic scattering modes of operation.
A third type of display medium is a colloidal suspension of dielectric needles. This type of display medium was described by A. M. Marks, "Electro-optical Characteristics of Dipole Suspensions," Applied Optics, 8, 1397 (1969).
Although there has been some investigation of liquid crystal dynamic scattering mode reflective displays (see U.S. Pat. No. 3,499,702 by Goldmacher et al; U.S. Pat. No. 3,592,527 by Conners et al; and U.S. Pat. No. 3,625,591 by Freiser et al), most of the research and engineering effort has been directed toward transmissive rather than reflective displays. A reflective display utilizing ambient light is highly advantageous since no display light source is required, as in most transmissive displays. Thus the size, power consumption, and cost of a reflective display utilizing ambient light may be less than a similar transmissive display.
To be successful, a reflective display should be visible throughout a relatively wide viewing angle range. This allows several observers to view the display simultaneously or the same observer to view the display from a variety of positions.